It's pointless to store these, since Nix knows where the logs are.
Also handle (in fact require) Nix's new log storage scheme. Also some
cleanups in the build page.
The singleton table SchemaVersion contains the current version
of the Hydra database schema. This can be used to upgrade the
schema on the fly.
Also reran the DBIx::Class schema loader.
releases as a dynamic view on the database was misguided, since
doing thing like adding a new job to a release set will invalidate
all old releases. So we rename release sets to views, and we'll
reintroduce releases as separate, static entities in the database.
the derivations that the jobset currently contains. This is
necessary to allow the "latest" channel to contain the correct
builds when the sources of a jobset are reverted.